Furuno CI-35 User manual

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FIRST EDITION :FIRST EDITION : FEB.FEB. 19971997
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iiiiiiiiiiiii i
"DANGER", "WARNING" and "CAUTION" notices appear throughout this manual. It is the
responsibility of the operator of the equipment to read, understand and follow these no-
tices. If you have any questions regarding these safety instructions, please contact a
FURUNO agent or dealer.
SAFETY INSTRUCTIONS
DANGER
This notice indicates a potentially
hazardous situation which, if not
avoided, will result in death or
serious injury.
This notice indicates a potentially
hazardous situation which, if not
avoided, could result in death or
serious injury.
This notice indicates a potentially
hazardous situation which, if not
avoided, could result in minor or
moderate injury, or property damage.
CAUTION
WARNING

ii
Do not disassemble or modify the
equipment.
Fire, electrical shock or serious injury can
result.
Immediately turn off the power at the
ship’s mains switchboard if water or
foreign object falls into the equipment
or the equipment is emitting smoke or
fire.
Continued use of the equipment can cause
fire, electrical shock or serious injury.
Do not open the cover of
the equipment.
This equipment uses high
voltage electricity which can
shock, burn, or cause death.
Only qualified personnel
should work inside the
equipment.
WARNING
Do not place liquid-filled containers on
the top of the equipment.
Fire or electrical shock can result if a liquid
spills into the equipment.
Do not place heater near the equipment.
Heat can melt the power cord, which can
result in fire or electrical shock.
Do not operate the unit with wet hands.
Electrical shock can result.
Use the correct fuse.
Use of the wrong fuse can cause fire or
equipment damage.
CAUTION
A warning label is attached to the equip-
ment. Do not remove the label. If the
label is missing or damaged, contact
a FURUNO agent or dealer about
replacement.
WARNING
To avoid electrical shock, do not
remove cover. No user-serviceable
parts inside.
Name:WarningLabel(1)
Type:86-003-1011-0
CodeNo.:100-236-230

iii
CONTENTS
SAFETY INSTRUCTIONS ________________________________ i to ii
TABLES FOR RECORDING USER PRESETS _______________ v to x
CHAPTER 1. GENERAL_______________________________1-1 to 1-8
1. FEATURES ..................................................................................... 1-1
2. PRINCIPLE OF MEASUREMENT .................................................. 1-2
3. TIDE, NAV-TIDE & TIDE DIFFERENTIAL....................................... 1-5
CHAPTER 2. OPERATION _____________________________2-1 to 2-4
1. CONTROL PANEL LAYOUT ........................................................... 2-1
2. FUNCTION OF KEYSAND CONTROLS........................................ 2-2
3. OPERATING PROCEDURE ........................................................... 2-4
CHAPTER 3. DISPLAY _______________________________3-1 to 3-18
1. DISPLAY SAMPLES ....................................................................... 3-1
2. HOW TO READ THE DISPLAY ...................................................... 3-2
FUNDAMENTAL DATA SECTION ..................................................... 3-3 to 3-8
SHIP’S SPEED/COURSE Display...................................................... 3-3
TRACKING MODE Display ................................................................ 3-4
ERROR Status Display....................................................................... 3-5
TIDE SPEED/DIRECTION Display..................................................... 3-6
PRESENT TIME Display .................................................................... 3-8
TRIP TIME/DISTANCE Display .......................................................... 3-8
DRIFT/TIDE DIF SECTION ..................................................................... 3-9
SET & DRIFT Display......................................................................... 3-9
TIDE DIFFERENTIAL Display ............................................................ 3-9

iv
TIDE VECTOR/COURSE PLOT SECTION.....................................3-10 to 3-15
TIDE VECTOR Display...................................................................... 3-10
TIDE HISTORY Display......................................................................3-11
COURSE PLOT Display .................................................................... 3-12
TIDE EFFECT Display....................................................................... 3-13
DRIFT Display ................................................................................... 3-15
HEAD-UP/NORTH-UP Presentation ................................................. 3-15
RANGE CURSOR ............................................................................. 3-15
ECHO LEVEL SECTION........................................................................ 3-16
ECHO LEVEL Display ....................................................................... 3-16
MISCELLANEOUS DATA ...............................................................3-17 to 3-18
WATER TEMPERATURE Display ..................................................... 3-17
MISCELLANEOUS DATA Display ..................................................... 3-18
CHAPTER 4. SETTING OPERATING CONDITIONS ________4-1 to 4-16
1. BASIC MENU.................................................................................. 4-1
MENU 1 .............................................................................................. 4-2
MENU 2 .............................................................................................. 4-4
MENU 3 .............................................................................................. 4-6
MENU 4 .............................................................................................. 4-8
2. RANGE SET MENU....................................................................... 4-10
3. ALARM SET MENU ....................................................................... 4-11
CHAPTER 5. TROUBLESHOOTING _____________________5-1 to 5-4
1. SELF-CHECK ................................................................................. 5-1
2. ERROR INDICATION...................................................................... 5-4
3. INTERNAL BATTERY ..................................................................... 5-5
SPECIFICATION___________________________________AP-1 to AP-5

v
TABLES FOR RECORDING USER
PRESETS
The CI-30/35H provides menus to preset, various measuring and display conditions to customize
the equipment precisely for your operating conditions.
The form below is provided to record user presets, so they can be restored in the event of loss by
misoperation or by maintenance/service work.
1) BASIC MENU (Display/measuring conditions)
[MENU 1]
ITEM USER PRESET : selected
REF TIDE DIF
TIDE AVERAGE
TIDE HISTORY
LAYER1
LAYER2
LAYER3
TIDE DIF DSP
DRIFT DSP
TEMP DSP
ECHO LEV DSP
BACKGROUND
*LAYER1 LAYER2 LAYER3
0 min
15 sec
1 min
1 min 2 min
5 min
3 min
10 min 4 min 30 min 5 min
1 hour
ON
ON
ON
ON
DRIFT
ON
COLOR
NORMAL
OFF
OFF
OFF
OFF
SPEED
OFF
GRAPH
1
OFF
23
FAC. SETTING
LAYER1
2 min (**)
15 sec
ON
ON
ON
ON
DRIFT
ON
COLOR
NORMAL
(**) “2 min” or longer averaging time is desirable to obtain stable and
smooth response of tide/tide differential display.
[MENU 2]
ITEM USER PRESET : selected
REF DEPTH
MENU SELECT
*OFF
LOCK E/S
UNLOCK
FAC. SETTING
OFF
LOCK
[MENU 3]
ITEM USER PRESET : selected
SHIP SPD AVE
DRAFT
WT SPD DEPTH
HEEL ANGLE
TRIM ANGLE
GT SPD CALIB
WT SPD CALIB
BEARING CALIB
EXT KP1 DIST
EXT KP2 DIST
BTM TIDE TRK
*15 sec
[ ] m
[ ] m
[ ] °
[ ] °
[ ] %
[ ] %
[ ] °
[ ] m
[ ] m
OFF
30 sec 60 sec
0.0 to 25.6 m
0.0 to 25.6 m
-12.8 to +12.7°
-12.8 to +12.7°
-12.8 to +12.7%
-12.8 to +12.7%
-12.8 to +12.7°
0.0 to 25.6 m
0.0 to 25.6 m
ON
FAC. SETTING
15 sec
0.0 m
2.0 m
0.0°
0.0°
0.0%
0.0%
0.0°
0.0 m
0.0 m
OFF
*
*
*
*
*
*
*
*
*
90 sec

vi
ITEM USER PRESET : selected
TIME DATA
WT SPEED
NAV FORMAT
NAV AID
NAV DATA
TIME INT
CRS CAL MODE
CRS CAL EXEC
TIDE OUT INT
*INT
T/D
CIF
EXT
NAV-TIDE
NMEA
GPS
LORAN-C
FAC. SETTING
INT
T/D
CIF
ALL
SPD
1 min
MAN
- -
15 sec
*
*
*
*
*
*
*
DECCA DR
LORAN-A
ALL
L/L
[ ] min
GT
START
SPD
1 to 10 min (in 1 min steps)
NAV
To start calibration, select START and press EVENT key.
15 sec 30 sec 1 min 2 min 5 min 10 min
MAN
2) RANGE MENU (Speed/distance/depth ranges)
ITEM USER PRESET
SPEED RANGE
DIST RANGE
ECHO DEPTH
ECHO SHIFT
[ ] kt
[ ] NM
[ ] m
[ ]
1.0 to 30.0 kt
0.1 to 5.0 NM
50 to 700 m
1 to 36
FAC. SETTING
2.0 kt
1.0 NM
50 m
1
3) RANGE MENU
ITEM
1ST LAYER
2ND LAYER
3RD LAYER
SHALLOW T/D
DEEP T/D
SHIP SPEED
TRIP
SET ON/OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
MIN
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] NM
[ ]
FAC. SETTING
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SET OFF / SP ON
SPD
DIR
SPD
DIR
SPD
DIR
SPD
DIR
SPD
DIR
SPD
CRS
DIST
TIME
MAX
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] kt
[ ]°
[ ] NM
[ ]
SP ON/OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
ON OFF
Marks on the ALARM MENU
Filled star ( ) : alarm active Hollow star ( ) : alarm inactive
Active speaker ( ) : speaker enabled Inactive speaker ( ) : speaker disabled
Note: 1. Descriptions of menu items and the procedures for presetting them begin on page 4-1.
2. To clear user presets and automatically restore factory settings, select “FACTORY” on
the BASIC MENU2- “MENU SET”. (Note that the user presets for “TEMP DSP” and
“ECHO LEV DSP” in MENU1 are not cleared by this operation.)
3. Items marked with “ ” are user changeable.
Items marked with “*” should not be changed needlessly once they are set at installa-
tion. Needless change can degrade the accuracy of measurements.

vii
[READ THIS FIRST!!]
IMPORTANT NOTICE ON TIDE MEASUREMENTS
(In nav-aided mode, tide accuracy depends heavily on gyro accuracy.)
SETTING SHIP’S HEADING
The CI-35/35H has the nav-aided mode to measure absolute tides even in deep waters where ground
tracking is unattainable. To achieve reliable measurements, however, you must supply accurate
heading (gyro) information and ship’s position (or speed/course) data to the CI-35/35H.
If you are going to use nav-aided mode, set the reading of theAD converter (gyro interface) exactly
with that of master gyrocompass.
Procedure
1. Confirm that the gyrocompass has settled and all the necessary compensations (latitude com-
pensation, weather compensation, etc.) are made correctly.
2. Manipulate the AD converter to obtain the same reading as you read on the master gyrocom-
pass. (Do not make adjustment while the ship is turning.)
If the gyro reading is accurate enough, the CI-35/35H should provide accurate tide information. If
the gyro data contains some error, however, you may see the following symptoms.
¡Set/drift information on nav-aided mode differs from that on ground-tracking mode.
¡Tide/tide differential information on nav-aided mode differs from that on ground-tracking
mode.
0
10
20 10 20
1°
0.2 kt
GT Mode
0
10
20 10 20
-3°
0.5 kt
NAV Mode GT Mode NAV Mode
If you encounter with such symptoms, perform the calibration following the procedure on the next
page.
Master
Gyrocompass AD Converter
(Gyro Interface)

viii
CALIBRATING COURSE OFFSET (Automatic)
A. When ground-tracking is attainable:
1. Make sure the navaid (GPS) is working correctly and accurately.
2. On CI-35/35H, select ground tracking mode. (Press the TRACKING MODE key to see the
“GT” mode indication on the display.)
3. In Menu 4, set ‘CRS CAL MODE’ to “GT”.
4. Run your boat at a speed about 10 kts, keeping the same direction.To minimize the effect of
gyro speed error, it is desirable to run along parallels (i.e., eastward or westward).
5. In Menu 4, place the cursor on “START” (‘CRS CAL EXEC’) and then press the EVENT
key.As soon as you press the EVENT, “0.0” should appear in reverse text at the upper-right
part of the display. After 2 mile-run, the display will show the course calibration angle
(result of calculation) in normal text.
Lead run 2 n.m. (approx) Course calib. angle
calibrated to fit these
two courses made good
Course made good
by ext. navaid (GPS)
Course made good
by CI-35/35H plus Gyro
Start Point
EVENT
pressed
B. When ground-tracking is unattainable:
1. Make sure the navaid (GPS) is working correctly and accurately.
2. On CI-35/35H, select nav-aided mode. (Press the TRACKING MODE key to see the “NAV”
mode indication on the display.)
3. In Menu 4, set ‘CRS CAL MODE’ to “NAV”.
4. Run your boat at a speed about 10 kts, keeping the same direction.To minimize the effect of
gyro speed error, it is desirable to run along parallels (i.e., eastward or westward).
5. In Menu 4, place the cursor on “START” (‘CRS CAL EXEC’) and then press the EVENT
key.As soon as you press the EVENT, “0.0” should appear in reverse text at the upper-right
part of the display.
6. When the boat has run for 5 minutes, turn your heading almost 180˚ and steer back to the
start point.After 10 minute-run, the display will show the course calibration angle (result of
calculation) in normal text.
Start Point
EVENT
pressed
Lead run
5 minutes
(half way)
off the track by 5 to
10° not to get on
own wake
calibrated to equalize
these tides

ix
WHY IS GYRO DATA IMPORTANT IN NAV-AIDED MODE?
If you consider the difference of tide vector calculations is ground-tracking mode and in nav-aided
mode, you will realize how important the gyro (heading) information is.
Tide Calculation in Ground-Tracking Mode
In ground-tracking mode, the CI-35/35H derives
tide information from the following data.
(1) Ship’s speed/course based on ground
(ground speed)
(2) Ship’s speed/course based on target layer
(water speed)
(3) Bearing of ship’s bow
(Heading by gyro)
Both ground speed (1) and water speed (2) are
sensed by the common transducers mounted on the
hull. Thus, they are the speed vectors with respect
to the ship’s bow. No matter what the true bearing
of ship’s heading be, the relative angle of these two
vectors does not change. The tide vector is simply
given as the difference of these two speed vectors.
The heading data by gyro (3) is used after the tide
vector calculation just to express the vector direc-
tions in true bearings (north referenced).
Even if the gyro data contains error, the sizes and
relative angles of vectors do not change. The gyro
erroronlyaffectsthebearingindicationofeachvec-
tor.
True north
eGyro
reading
Ship’s bow
wWater speed
vector
qGround speed
vector
Tide Vector
=
Without gyro error
True north
Tide Vector
eGyro
reading
Ship’s bow
wWater speed
vector
qGround speed
vector
With gyro error
Gyro
error
True bearing of each speed vector contains
fixed error. But, their sizes and relative angles
are maintained despite the gyro error.
: True bearing of ship’s bow (ref. north)
: Gyro reading
: Direction of ground speed (ref. bow)
: Direction of water speed (ref. bow)
A
θ
A
θ
H
θ
H
θ
G
θ
G
θ
W
θ
A
θ
H
θ
G
θ
W
θ
W
θ

x
Tide Calculation in Nav-Aided Mode
In nav-aided mode, the CI-35/35H derives tide information from the following data.
(1) Ship’s speed/course sensed by the external navigator (GPS)
(nav speed = pseudo ground speed)
(2) Ship’s speed/course based on target layer
(water speed)
(3) Bearing of ship’s bow
(Heading by gyro)
Here,navspeed(1) is the ship’s speed vector sensed
by the external navigator, and the moving direc-
tion is expressed with respect to true north.
While the water speed (2) is the ship’s speed vec-
tormeasuredbyCI-35/35H using the Doppler shifts
against the measuring layer, and accordingly its di-
rection is expressed with respect to the ship’s bow.
As the directional reference of these two vectors
are different (north vs ship’s bow), we can not sim-
ply calculate the difference of vectors to obtain the
tide vector in question.
So the direction of water speed vector (2) is con-
verted to true bearing (north reference) by using
the gyro data, and then the tide vector is calculated.
If the gyro data contains some error, the true bear-
ing of the water speed vector changes (rotates) ac-
cordingly.Whilethebearing of the nav speed vector
does not change with the gyro error. (The relative
angle of these two changes.)
In other words the tide vector, given as a differ-
ence of these two speed vectors, changes in size
(speed) and bearing by the gyro error. (Error in size
and bearing mean the tide vector is unreliable and
useless.)
You may now realize that the gyro data in nav-aided
mode is very important and it has to be accurate
enough for reliable tide data.
To obtain dependable tide/tide differential data, it
is desirable to reduce the gyro error below 1 de-
gree.
True north
eGyro
reading
Ship’s bow
wWater speed
vector
qNav speed
vector
Tide Vector
=
Without gyro error
True north
Tide Vector
eGyro
reading
Ship’s bow
wWater speed
vector
qNav speed
vector
With gyro error
Gyro
error
Relative angle of water speed vector and
nav speed vector changes with gyro error.
Accordingly, the size (speed) and direction
of tide vector change.
: True bearing of ship’s bow (ref. north)
: Gyro reading
: True bearing of nav speed (ref. north)
: Direction of water speed (ref. bow)
A
θ
H
θA θ
H
θ
N
θ
N
θ
W
θ
A
θ
H
θ
N
θW
θ
W
θ
Note: The depth must be at least 40 m in order to calculate tide.

1-1
CHAPTER 1. GENERAL
1. FEATURES
¡The functions of CI-35 and CI-35H are same. CI-35H is type approved by MOT (Ministory of
Transportation).
¡Even in deep waters where ground (bottom) reference is not available acoustically, the CI-35/
35H can provide absolute movements of measuring layers by receiving position (or speed) data
from GPS navigator and heading data from gyro compass. It may be used on deep sea fishing
boats or on ocean research vessels.
¡The CI-35/35H consists of three major units; display unit; transceiver unit and hull unit (trans-
ducer), each compact enough to permit installation even on a small boat.
¡Triple-beam system for automatic error compensation against pitching and rolling of vessel.
Single-mold transducer makes installation easy while maintaining mechanical beaming accu-
racy.
¡Sounding frequency of 130 kHz provides high interference immunity from other acoustic equip-
ments. Intelligent digital signal processing technique adds tracking stability and measuring ac-
curacy.
¡Echo level display always on screen. Permits constant monitoring of signal conditions of three
sounding beams.
¡Tide effect display plots movements of tides beneath the vessel’s course track. Helpful in esti-
mating three-dimensional deformation of cast net.
¡Tide history display presents change of tide over last 24 sample points (24 hours maximum)
¡Raw data output port provided for collecting and analyzing current data on a separate computer.
Note: When transmitting with the external transmission pulse (KP) taken from an external device
(echosounder, sonar, etc.), the repetition rate of the KPshould be more than 500 ms. The repetition
rate may become shorter than 500 ms when the range setting on the external device is less than 100
m. Therefore, set the range on the external device to more than 100 m.

1-2
2. PRINCIPLE OF MEASUREMENT
When a moving vessel emits an acoustical pulse into the water at an angle, a portion of emitted
energy is reflected from the seabed and other microscopic objects in the sound path, such as plank-
ton or air bubbles. The frequency of the received signal is shifted from the transmitted frequency in
proportion to relative velocity between the vessel and underwater reflecting objects. This is called
Doppler Effect.
The CI-35/35H calculates and displays movements of ship and currents at specific depths by mea-
suring Doppler shifts obtained from three separate directions.
Planktonic layer
Seabed
Frequency of reflected signal is
shifted in proportion to relative speed
between the vessel and reflecting
objects.
Ship’s Speed (Here, speed is a vector value including velocity and direction.)
Depending on the base of measurement, ship’s speed is expressed in two ways:
Ground tracking speed: Ship’s speed and course relative to seabed (fixed base)
(Absolute speed)
Water tracking speed: Ship’s speed and course relative to water layer just below the
vessel (floating base)
(Relative speed)
Nav-aided speed: Ship’s speed and course obtained by external navigation
equipment (GPS)
(Absolute speed)
Fixed
GPS satellites Nav-aided speed
(Pseudo ground tracking speed)
Water tracking speed
Ground tracking speed
Near-surface layer
:Base of measurement

1-3
Tide
Tide is movement of watermass at a particular depth.
To know absolute tide (speed on ground), the following two data are required:
1Ship’s speed and course based on ground
2Ship’s speed and course based on measuring layer (A)
Absolute tide is, then, given as a difference of these two speed vectors.
Absolute Tide = 1- 2
Fixed
Layer (A)
:Base of
measurement
q
w
Nav-Tide
Nav-Tide is an absolute movement of watermass at a particular depth, taking speed information
from the external navigator (GPS) as a pseudo ground tracking speed.
To calculate Nav-tide, the following two data are required:
1Ship’s speed and course obtained by external navigation equipment (GPS)
2Ship’s speed and course based on measuring layer (A)
Nav-tide is, then, given as a difference of these two speed vectors.
Absolute Tide = 1- 2
GPS satellites qNav-aided speed
(Pseudo ground tracking speed)
wWater tracking
speed
Layer (A)
:Base of measurement

1-4
Tide Differential
Tide differential is a relative movement of tides at different depths, layer (A) and layer (B).
To calculate tide differential, the following two data are used:
1Ship’s speed and course based on layer (A)
2Ship’s speed and course based on layer (B)
Tide differential between two layers is, then, given as a difference of these two speed vectors.
Tide Difference = 1- 2(Movement of layer B based on layer A)
or
= 2- 1(Movement of layerA based on layer B)
w
Layer (B) :Base of measurement
qLayer (A)

1-5
3. TIDE, NAV-TIDE & TIDE DIFFERENTIAL
Tide
(Absolute tide)
Absolute tide can be measured in the ground tracking mode.
:Base of
measurement
w
q
Layer A
Fixed
Start of
trip End of trip
(Moving at 10 kt on ground)
(Moving at 3 kt on ground)
10 NM (1 hour trip)
Assume that the ship and layer A are moving in the same direction, and ship’s speeds based on
ground (Vg) and on layerA (Vwa) are measured as;
Vg = 10 kt (Ship’s speed based on ground)
Vwa = 7 kt (Ship’s speed based on layer A).
Speed of layerA based on ground (C1) can be calculated as follows:
C1 = Vg - Vwa
= 10 - 7
= 3 (kt)
Nav-Tide (Absolute tide)
Absolute tide can be measured in the nav-aided mode.
Nav-aided ship’s speed (Vn) is equivalent to ship’s ground tracking speed in the ideal conditions.
That is, the nav-tide can be calculated by simply replacing Vg with Vn in the above equation.

1-6
Tide Differential
Tide differential is a relative movement of tides at different depths.
It can be measured in the ground tracking, water tracking and nav-aided modes.
:Base of measurement
w
e
Layer A
Start of
trip End of trip
(Moving)
10 NM (1 hour trip)
Layer B
(Moving)
2 kt
5 kt
Assuming that the ship, layer A and layer B are moving in the same direction, and ship’s speeds
based on layerA (Vwa) and on layer B (Vwb) are measured as;
Vwa = 8 kt (Ship’s speed based on layer A)
Vwb= 5 kt (Ship’s speed based on layer B)
Tide differential calculations in ground tracking mode
As an absolute ship’s speed (Vg) is available in the ground tracking mode, tide speeds of layer A
(C1) and layer B (C2) based on ground are calculated as follows:
C1 = Vg - Vwa (Speed of layer Abased on ground)
C2 = Vg - Vwb (Speed of layer B based on ground)
Thus, the tide differential (Cd) between layer A and layer B is;
Cd = C2 - C1
= (Vg - Vwb) - (Vg - Vwa)
= Vwa - Vwb
= 8 - 5
= 3 (kt)
or
Tide differential based on layer A
Speed of layer B viewed from
layer A

1-7
Cd = C1 - C2
= (Vg - Vwa) - (Vg - Vwb)
= Vwb - Vwa
= 5 - 8
= -3 (kt)
In the water tracking mode, watermass just below the transducer (near-surface layer) is taken as the
base of all measurements (virtual ground). Therefore, the ship and tide speeds in the water tracking
mode are not absolute but relative to this near-surface layer.
Vw = 9 kt (Ship’s speed based on near-surface layer)
Vwa = 8 kt (Ship’s speed based on layer A)
Vwb= 5 kt (Ship’s speed based on layer B)
:Base of measurement
we
Layer A
Start of
trip End of
trip
10 NM (1 hour trip)
Layer B
2 kt
5 kt
q
Near-
surface
layer
1 kt Assume that the ship and all measuring layers
are moving in the same direciton, but at different
speeds.
Tide differential based on layer B
Speed of layer A viewed from
layer B

1-8
Tide differential calculations in water tracking mode
Tide speeds of layerA (C1) and layer B (C2) relative to near-surface layer (Vw) are calculated as
follows:
D1 = Vw - Vwa (Speed of layer Abased on near-surface layer)
D2 = Vw - Vwb (Speed of layer B based on near-surface layer)
The tide differential (Dd) between layers Aand layer B is;
Dd = D2 - D1
= (Vw - Vwb) - (Vw - Vwa)
= Vwa - Vwb
= 8 - 5
= 3 (kt)
or
Dd = D1 - D2
= (Vw - Vwa) - (Vw - Vwb)
= Vwa - Vwb
= 5 - 8
= -3 (kt)
If you compare the results of calculations on this page with the ones on preceding pages, you will
find the tide differential of two layers is identical irrespective of tracking mode.
Tide differential based on layer A
Speed of layer B viewed from
layer A
Tide differential based on layer B
Speed of layer A viewed from
layer B